1. Technical Field
The present invention concerns a method of detecting electric variables of a three-phase AC network having first, second and third phases. The invention further concerns a method of feeding electric energy into an electric AC network. The present invention further concerns a device for detecting electric variables of a three-phase AC network and a device for feeding electric energy into an electric AC network. The invention also concerns a wind power installation which is adapted to detect electric variables of an AC network and/or to feed electric energy into an electric AC network.
2. Description of the Related Art
Particularly to feed electric energy into an existing electric AC network it is necessary to have as accurate knowledge of it as possible. Knowledge of the frequency of the AC voltage in the network and the magnitudes and phases of the voltages are of significance. For other purposes however also, which can be related to the feed into the network, such as for example detecting troubles in the network, detection which is as accurate as possible and in as real-time relationship as possible primarily of the electric voltages of the network is desirable.
To detect frequency and phase angle of the AC voltage of an AC network zero passages of the voltage are usually detected. The time spacing of two adjacent voltage zero passages corresponds to half a period duration, and the frequency can be calculated therefrom. Thus it is also possible to determine the phase position from the zero passage and the frequency or the two zero passages.
A disadvantage in that respect is in particular that at least the time duration of half a period is correspondingly necessary in order to detect frequency and thus changes in frequency. At the same time the quality with such measurement methods may be inadequate. Particularly for AC networks which are increasingly fed and also supported by decentral energy supply means, measurement which is as quick as possible with the highest possible quality is of significance. Reliable and rapid detection of network troubles such as the occurrence of short circuits is also increasingly gaining in significance.
Therefore the object of the invention was to propose a method which is improved in respect of at least one of the aforementioned disadvantages and a corresponding device. In particular the invention seeks to propose a measurement method which is improved as much as possible in respect of speed and quality. At the least an alternative measurement method and an alternative method of feeding energy and corresponding devices were to be proposed.
As state of the art attention is directed at this juncture generally to the following documents: DE 101 13 786 A1, EP 004 984 A1 and DE 199 44 680 A1.